Process of flooding oil-bearing formations using aldehydes as oxygen scavengers in polymer solutions

ABSTRACT

Flooding of oil-bearing subterranean formations with aqueous solutions of partially hydrolyzed, high molecular weight polyacrylamides or copolymers of acrylamide and acrylic acid wherein the aqueous solution contains at least 0.1 ppm of dissolved oxygen and the oxygen adversely influences the mobility imparted by the polymer, is improved by incorporating 5-1000 ppm of a water-soluble aldehyde (preferably formaldehyde) into the aqueous solution to form a complex with the oxygen and thereby inhibit the adverse effects of the oxygen.

FIP7912 United States Patent 91 1 Apr. 2, 1974 Knight PROCESS OF FLOODING OIL-BEARING 3.053.765 9/1962 252/865 D FORMATIONS USING ALDEHYDES AS g ggg'ggg 413 g 2 4: OXYGEN SCAVENGERS IN POLYMER 3:106:525 l0/l963 Schmid et ah)... D SOLUTIONS 3,625,888 12/1971 Redmore et al.. 25218.55 o 7 5 Inventor; Bruce L. Knight, Limemn (301m 1 3,634,232. l/ l972 Dunlop 252/855 D X [73] Assignee: g f z Company Primary Examiner-Stephen J. Noi'asad I v Attorney, Agent; or Firm-Joe C. Herring; Richard C. [22] Filed: Aug. 28, 1972 Willson, Jr.; Jack L. Hummel 211 Appl. No.: 284,204 T I RelatedUS. Application Data [57] ABSTRACT {63] Continuatiomimpa" of Sen N0 19 558 OCL 21 Flooding of oil-bearing subterranean formationswith l97l, abandoned, which is a continuation in-part 0i aqueous Solutions of P i l y hydrolyzed, high molec- Ser. No. [17,692, Feb. 22, 197i, abandoned. welght polyacfyiamldes 0r QP Y 0f amylamide and acrylic acid wherein the aqueous solution i521" us. 01...... 166/305 R,.-l66/273, 166/274 contains at least pp of dissolved Oxygen and the 51,} Int. Cl E21!) 43/22 Oxygen adversely influences the mobility imparted y 581' Field of Search 166/273-275, the Polymer, is improvei by i v' s 5-1000 1 /305 252/ 55 D ppm of a water-soluble aldehyde (preferably formalt dehyde) into the aqueous solution to form a complex {3 m-di Cited H with the oxygen and thereby inhibit the adverse effects UNITED STATES PATENTS. f 2,827,964 3/l958 Sandiford et al. l6l274 18 Claims, N0 Drawings or reservoir temperature. Of course, other aldehydes can be substituted for the formaldehyde or paraformaldehyde in the above reactions.

Concentrations of about 5 to about L000 ppm and preferably about 25 to about 750 ppm and more preferably about 50 to about 500 ppm of the aldehyde are useful within the aqueous polymer solution. Of course, an increase oxygen concentration within the aqueous polymer solution will generally demand a larger concentration of aldehyde within the solution. The aldehyde can be in concentrations of at least greater than the stoichiometric amount needed to react with the available oxygen within the aqueous system. Generally speaking, about 50 to about 200 ppm of formaldehyde in the aqueous polymer solution is useful to inhibit oxygen degradation in most reservoirs. In addition, sufficient aldehyde may be incorporated within the aqueous polymer solution to act as a bactericide. However, the above concentration ranges are generally effective to take care of the available oxygen as well as the bacteria. The formaldehyde can be introduced into the system as an aqueous solution of formaldehyde, e.g., 27-40 percent concentration.

The minimum concentration of dissolved oxygen in the water that adversely influences mobility control of aqueous polymer solutions is above about 0.1 and generally above about 0.5 ppm. Concentrations'abo've l.0 ppm and up to 8-l0 or more ppm are generally characteristic of aqueous polymer solutins. 'Of c0urse the upper limits of oxygen concentration in the water will depend on temperature, viscosity, etc. The degree of adversity is directly dependent on the oxygen concentration.

The polymers applicable with this invention include partially hydrolyzed high molecular weight polyacrylamides, copolymers of acrylamide and acrylic acid or alkali metal salts thereof, and partially hydrolyzed products of these copolymers. Specific examples of the partially hydrolyzed polyacrlamides are found in U. S. Pat. Nos. 2,827,964 to Sandiford; 3,039,529 to McKinnon; and 3,282,337 to Pye. Examples of preferred copolymers include those of acrylamide and sodium acrylate and partially hydrolyzed products thereof. Preferably the polymers have average molecular weights above one million and more preferably above -10 million.

EXAMPLES The following examples are presented to teach specific embodiments of the invention. The percents are based on volume, unless otherwise specified. Also, viscosities are measured at ambient temperature. The screen factor" used in the examples is determined by the method taught in SPE Paper 2867, titled Factors Influencing Mobility Control by Polymer Solution,"v Jennings et al., copyright l970-the screen factor is a measure of the time a given volume of polymer solution flows through a porous medium (usually a pack of five lOO-mesh stainless steel screen in close contact) compared to the flow time for the same volume of water through the same mediumi The "screen factor correlates flow resistance in a porous medium for a given polymer class becauseit is sensitive to changes in molecular weight and structure, the latter factors are of great importance in mobility control.

EXAMPLE l Three samples are obtained by mixing 700 ppm of Dow 700 series Pusher polymer (a partially hydrolyzed, high molecular weight polyacrylamide marketed by S.O.R.D., Dow Chemical Co.-, Midland, Mich.) with water containing about 555 ppm of total dissolved solids, analyzed as: Component Ntrl' so=. ll5 Total 555 The water is filtered through a 0.1 micron filter to inhibit bacteria formation, but is not tie-oxygenated.

The samples are prepared in a pure nitrogen atmosphere at 23C and are stored at 50C in dark bottles in a pure nitrogen atmosphere. The screen factors and viscosities of the samples are periodically measured at 23C to determine the degradation of the solutions due to dissolved oxygen (concentration about 9-10 ppm before the hyposulfite or formaldehyde is added within the water. Sample 1 contains no additives and serves as a blank for comparative purposes. Sample 2 contains 50 ppm of sodium hyposulfite. Sample 3 con tains 200 ppm of an equilibrium mixture of formaldehyde and paraformaldehyde. The screen factors and viscosities are measured periodically until stability of the readings is observed. Also, the preparation and storage of the samples are carried out in such a manner as to preclude the possibility of bacterial degradation. Hence, all observed degradation is assumed to be due to the presence of oxygen. Table 1 indicates the screen factors and viscosities of the three samples over the indicated times:

PPM i35- Viscosity, cp

Screen Factor Loss 329: Viscosity Loss 8? 0 Sample 2: 50 ppm. Sodium Hyposulfite Time. Days Screen Factor cp 33 23.3 Sample 3: 200 ppm Formaldehyde Time, Days Screen Factor Viscosity,

Screen Factor Loss Viscosity Loss-=- 0 Viscosity,

Screen Factor Loss 5% Viscosity Loss 0.67:

' white, the total screen factor loss is 4 percent and the viscosity lossv is 0 percent. With sample 3, the total screen factor loss is 5 percent whereas the viscosity loss PROCESS OF FLOODING OIL-BEARING FORMATIONS USING ALDEIIYDES AS OXYGEN SCAVENGERS IN POLYMER SOLUTIONS CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of my copending application, Ser. No. l9 1 ,558, filed Oct. 2 l, l97l now abandoned; which is a continuation-in-part of Ser. No. l l7,692. filed Feb. 22. I971, also now abandoned.

1. Field of the Invention.

This invention relates to flooding oil-bearing subterranean formations with aqueous polymer solutions containing dissolved oxygen. A water-soluble aldehyde,

e.g., formaldehyde is admixed with the solution to complex with the oxygen and inhibit the adverse effect of the oxygen upon the polymer flood.

2. Description of the Prior Art.

it is known in the art that formaldehyde will react with polyacrylamde as taught in Water-Soluble Resins, edited by Robert L. Davidson and Marshall Sittig, Reinhold Book Corporation, copyright l962, page 180. This article teaches that the polyacrylamide reacts with formaldehyde to form methylolated polyacrylamide.

US. Pat. No. 3,085,062 to Turbak teaches that 0.005'-5 percent of formalydehyeis useful to reduce viscosity loss, due to thermal degradation, during viscous waterflooding with viscosity-imparting agents such as sulfonated'polymers, copolymerized products of vinyl aromatics and maleic anhydrides, and synthetic polymers containing an aromatic ring, polyethylene oxide type or polypropylene oxide type.

U. S. Pat. No. 2,827,964 to Sandiford teaches the use of aldehydes as bactericides in aqueous solutions containing partially hydrolyzed, high molecular weight.

polyacrylamldes. Such give improved oil recoveries.

U. S. Pat. No. 3,042,61 l to Patton teaches improved .4

nounced stabilizing chemical effect at reservoirv ternperatures and even in the presence of rock surfaces, ions, etc.

U. 8. Pat. No. 2,702,791 to Teichmann teaches the use of formaldehyde to inhibit the deterioration of a tannin-dispersant in drilling fluids, Teichmann mentions that the deteriortion is due to oxygen within the drilling muds.

Partially hydrolyzed polyacrylamides and copolymers of acrylamide and acrylic acid or the alkali salts thereof have gained acceptance as very useful mobility reducing agents in secondary and tertiary oil recovery processes. The polymers reduce the mobility of the waterflood by reducing the relative permeability to the flow of water in the reservoir rock as well as increasing the viscosity of the water. Certain factors within the reservoir, however. tend to adversely affect the mobility reducing characteristics of the polymer solutions. The most common forms of degradation are bacterial action and oxygen-initiated free radical formation.

Sodium hyposulfite is used to overcome oxygen degradation; however, there must be a catalyst present, e.g.. salts of cobalt, copper, and nickel, to catalyze the reaction of hyposulfite with the oxygen. The catalyst can be present in the water; but, where not present, the

catalyst has to be added to effectively remove the oxygen.

Applicant has discovered that by incorporating water-soluble aldehydes, such as formaldehyde, within the aqueous system, the adverse effects of the oxygen can be overcome and improved mobility control is realized.

SUMMARY OF THE INVENTION adversely influences the mobility control-applicant has overcome this adversity by incorporating formaldehyde into the aqueous solution to complex with the oxygen. Concentrations of about 5 to 1,000 ppm of formaldehyde are useful in the aqueous solution.

PREFERRED EMBODIMENTS OF THE lNVENTlON This invention is especially useful with secondary and tertiary recovery methods wherein a displacing fluid is used.- to displace crude oil from a subterranean oilbearing reservoir. The displacing-fluid can be an immiscible displacing fluid, a miscible or miscible-like displacing fluid followed by an aqueous solution containing a mobility reducing agent andthis, in turn, optionally followed by a drive fluid. An example of an immiscible flood includes an aqueous waterflood having a mobility reducing agent incorporated into a portion thereof to impart mobility control to the process. Examples of miscible and miscible-like flooding processes include injecting a firstdispla'cing fluid, e.g., an emulsion, a micellar dlspersioman oil-miscible fluid, soluble oil, etc. and thisin tum followed by an aqueous slug containing a mobility reducing agent. Examples of useful displacing fluids include those defined in U. S. Pat. Nos. 3,254,714 and 3,275,075 to Gogarty et al.'. 3,497,006 to Jones et al.; 3,506,070 to Jones; 3,330,344, 3,330,348, and 3,330,6ll to Reisberg; 3,537,520 to Holm, etc.

The water-soluble aldehydes includev those aldehydes containing 1 to about 5 carbon atoms and which are water-soluble Preferably, the aldehyde is either paraformaldehyde or formaldehydeor an equilibrium mixture thereof. The aldehyde complexes'with the oxygen within the aqueous solvent and prevents degradation of the mobility control agent due to the oxygen. lt is postulated that this beneficial effect is due to the formation of a stable radical species upon reaction with oxygen; such is illustrated by the following formulae (Formula I is with fonnaldehyde and Formula 2 is with perforrnaldehyde):

EXAMPLE ll For a comparative study, treatment'of identical wells in a reservoir is performed. The same source of injection water is used throughout the testing and concentration of Dow 700 Pusher polymer throughout the testing is 335 ppm. Also. the procedure for injecting the water. etc.. is consistent in both tests. The chemicals are admixed with the water in a pipeline at a distance-of about one-half mile from the. wellhead. The aqueous polyacrylamide solution, absent dissolved oxygen. has a screen factor of 15.6 and a viscocity of 9.5 cp. Oxygen is taken up or sorbed by the water as it travels to the wellhead. Oxygen concentration at the wellhead is about ppm. i.e., this is the equivalent oxygen concentration before reaction with formaldehyde or hyposulfite. The data illustrated in Table 2 for the First Test" and Second Test" are obtained at the wellhead.

First Test The water is treated with 50 ppm of sodium hyposulfite and ppm of sodium pentachlorophenol, a bactericide, prior to addition of polymer. The results of this test are indicated in Table 2.

Second Test .-The above treatment was stopped. and sufficient time was allowed for the system to purge itself. Thereafter. the water was treated with 200 ppm of an aqueous formaldehyde solution containing 37 percent active formaldehyde. thus 74 ppm of formaldehyde, prior to addition of'polymer. The results of this treatment are indicated in Table 2.

TABLE 2 Screen Factor Viscosity. cp

Aqueous pulyacrylamide solution absent dissolved oxygen 15.6 9.5 First Test: After sodium hyposulfite sodium pcntuchlorophenol 5.2 5.5 Second Test: After formaldehyde 13.2 6.7

EXAMPLE ill The procedure. of Example 1 is repeated except the polymer solutions are stored at 22 C and the polymer is a copolymer obtained by a catalyzed aqueous reaction of 70 percent acrylamide and percent sodium acrylate; average molecular weight is about 12-15 million. Oxygen concentration is about 8-10 ppm and polymer concentration is 700 ppm. Results are shown in Table 3.

TABLE 3 With 50 ppm of formaldehyde Time. Days Screen Factor Viscosity. cp (RPM. 72 F) 0 g 25.4 39.6 6 26.5 38.4 I l 26.1 38.7 26 24.5 37.9 46 25.5 38.1 67 26.2 38.7 85 25.2 37.6 127 25.2 37.4 No formaldehyde present Time. Days Screen Factor Viscosity. cp (6RPM. 72 F) The above data clearly shows that the properties of the copolymer are improved with formaldehyde.

It is not intended that this application be limited by the specifies taught herein. Rather, all equivalents obvious to those skilled in the art are intended to be incorporated within the scope of the invention as defined within the specification and appended claims.

What is claimed is: V

1. A process of improving the mobility control of flooding an oil-bearing subterranean formation wherein an aqueous solution comprised of polymer(s) selected from the group consisting of partially hydroly'zed, high molecular weight polyacrylamides. copolymer of acrylamide and acrylic acid or alkali metal salts thereof. and partially hydrolyzed polymers of the copolymers is injected into the formation to improve the mobility control thereof and wherein the water contains at least about 0.1 ppm (based on the water) of dis solved oxygen which adversely affects the mobility control through degradation of the polymer, the improvement comprising incorporating into the aqueous solution sufficient amounts of aldehyde to complex with the oxygen and thus inhibit the adverse effect the oxygen has upon degrading the aqueous polymer solution.

2. The process of claim 1 wherein about 5 to about 1,000 ppm of formaldehyde is incorporated into the aqueous solution.

3. The process of claim 1 wherein about 25 to about 750 ppm of formaldehyde is incorporated into the aqueous solution:

4. The process of claim 1 wherein about 50 to about 500 ppm of formaldehyde is incorporated into the aqueous solution.

5. The process of claim 1 wherein the polymer has an average molecular weight of at least about one million.

6. The process of claim 1 wherein a slug of micellar dispersion is injected into the formation Previous to the injection of the polymer solution.

7. The process of claim 1 wherein the dissolved oxygen concentration-in the water is at least about 1.0

' 8. The process of claim -1 wherein the polymer is a partially hydrolyzed, high molecular weight polyacrylamide.

9. The process of claim 1 wherein the polymer is a copolymer of acrylamide and sodium acrylate.

10. A process of improving the mobility of control of an oil-bearing subterranean formation wherein an aqueous solution comprised of a partially hydrolyzed, high molecular weight polyacrylamide is injected into the formation and displaced therethrough to improve the mobilitycontrol of the flooding process and wherein the water contains at least about 0.1 ppm (based on the water) of dissolved oxygen which udversely affects mobility control through degradation of the polyacrylamide, the improvement comprising incorporating into the aqueous solution about to about 1,000 ppm of a water-soluble aldehyde to complex with the oxygen and thus inhibit the adverse influence the oxygen has upon degrading the aqueous polyacrylamide solution.

11. The process of claim 10 wherein the aldehyde is formaldehyde.

12. The process of claim 10 the aldehyde is an equilibrium mixture of formaldehyde and paraformaldehyde.

13. The process of claim 10 wherein the concentration of the aldehyde is about 25 to about 750 ppm, based on the aqueous solution.

14. The process of claim 10 wherein the. concentration of the aldehyde is about 50 to about 500 ppm, based on the aqueous solution.

15. A process of improving the mobility control of flooding an oil-bearing subterranean formation wherein an aqueous solution comprised of a copolymer of ucrylamide and acrylic acid or an alkali metal salt thereof is injected into the formation and displaced therethrough to improve the mobility control of the flooding process and wherein the water contains at least about 0.1 ppm (based on the water) of dissolved oxygen which adversely affects mobility control through degradation of the copolymer, the improvement comprising incorporating into the aqueous solution about 5 to about 1,000 ppm of a water-soluble aldehyde to complex with the oxygen and thus inhibit the adverse influence the oxygen has upon degrading .the aqueous copolymer solution.

16. The process of claim 15 wherein the aldehyde is formaldehyde.

17. The process of claim 15 wherein the aldehyde is an equilibrium mixture of formaldehyde and paraformaldehyde.

18. The process of claim 15 wherein the concentration of the aldehyde is about 50 to about 500 ppm.

based on the aqueous solution.

a k a :u n:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO- Dated 2,

Inventor(s) Bruce L. Knight It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r v q Coiumn 2, line 57: Delete "performaideh'yde" and insert --paraforma|dehyde--.

Column 6, line 17: Delete "specifies" and insert --specifics--. Coiumn 6, line 5] Deiete "Previous" and insert --previous--. Column 7, line 1 1 After 10" insert -'-wherein--.

Signed and sealed this 30th day of July 197A.

(SEAL) Attest:

McCOY M. GIBSON, JR. D I I C. MARSHALL DANN Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Petent No. 3,800,871 bated Apri] 2, 1974 Inventor(s) Bruce L. Knight It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 57: Delete "performa'ldehyde" and insert --paraforma1dehyde--.

Column 6, line 17: Deiete "specifies" and insert --specifics--.

Coiumn 6, line 5] Delete ".Previous and insert --previous--.

Coiumn 7, line 11: After "10" insert -wherein--.

Signed and sealed this 30th day of July 197 p.

(SEAL) Attest:

McCOY 1 1. GIBSON, JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. The process of claim 1 wherein about 5 to about 1,000 ppm of formaldehyde is incorporated into the aqueous solution.
 3. The process of claim 1 wherein about 25 to about 750 ppm of formaldehyde is incorporated into the aqueous solution.
 4. The process of claim 1 wherein about 50 to about 500 ppm of formaldehyde is incorporated into the aqueous solution.
 5. The process of claim 1 wherein the polymer has an average molceular weight of at least about one million.
 6. The process of claim 1 wherein a slug of micellar dispersion is injected into the formation Previous to the injection of the polymer solution.
 7. The process of claim 1 whereIn the dissolved oxygen concentration in the water is at least about 1.0 ppm.
 8. The process of claim 1 wherein the polymer is a partially hydrolyzed, high molecular weight polyacrylamide.
 9. The process of claim 1 wherein the polymer is a copolymer of acrylamide and sodium acrylate.
 10. A process of improving the mobility of control of flooding an oil-bearing subterranean formation wherein an aqueous solution comprised of a partially hydrolyzed, high molecular weight polyacrylamide is injected into the formation and displaced therethrough to improve the mobility control of the flooding process and wherein the water contains at least about 0.1 ppm (based on the water) of dissolved oxygen which adversely affects mobility control through degradation of the polyacrylamide, the improvement comprising incorporating into the aqueous solution about 5 to about 1,000 ppm of a water-soluble aldehyde to complex with the oxygen and thus inhibit the adverse influence the oxygen has upon degrading the aqueous polyacrylamide solution.
 11. The process of claim 10 wherein the aldehyde is formaldehyde.
 12. The process of claim 10 the aldehyde is an equilibrium mixture of formaldehyde and paraformaldehyde.
 13. The process of claim 10 wherein the concentration of the aldehyde is about 25 to about 750 ppm, based on the aqueous solution.
 14. The process of claim 10 wherein the concentration of the aldehyde is about 50 to about 500 ppm, based on the aqueous solution.
 15. A process of improving the mobility control of flooding an oil-bearing subterranean formation wherein an aqueous solution comprised of a copolymer of acrylamide and acrylic acid or an alkali metal salt thereof is injected into the formation and displaced therethrough to improve the mobility control of the flooding process and wherein the water contains at least about 0.1 ppm (based on the water) of dissolved oxygen which adversely affects mobility control through degradation of the copolymer, the improvement comprising incorporating into the aqueous solution about 5 to about 1,000 ppm of a water-soluble aldehyde to complex with the oxygen and thus inhibit the adverse influence the oxygen has upon degrading the aqueous copolymer solution.
 16. The process of claim 15 wherein the aldehyde is formaldehyde.
 17. The process of claim 15 wherein the aldehyde is an equilibrium mixture of formaldehyde and paraformaldehyde.
 18. The process of claim 15 wherein the concentration of the aldehyde is about 50 to about 500 ppm, based on the aqueous solution. 